1. Field of the Invention
The present invention relates to display systems and, more particularly, is directed towards computer displays, TV displays, digital image processing, radiographic instrumentation, two-dimensional spatial matched filtering, sampled-data reconstruction (interpolation and smoothing), optical image processing, solid-state imaging array display and low-bandwidth TV picture transmission and reception.
2. Description of the Prior Art
Two-dimensional images that have been spatially-sampled, for example in computer processing, generate display artifacts due to aliasing, leakage and data quantization if the digital image data is simply converted to analog intensity values and is displayed directly. These artifacts seriously degrade the quality of image perception. The well-known electrical communication theory solution to minimize display artifacts includes the use of a sharp cut-off low-pass filter having a sin x/x weighting function (impulse response) with zeroes matched to the sampling intervals. In addition, an aliasing filter is employed before sampling to satisfy the band-limiting requirements (Nyquist Limit) of the classical sampling theorem.
However, implementation of this theoretically-optimum technique for sampled-data reconstruction, interpolation and smoothing is often impractical even for one-dimensional data because (1) the sin x/x response requires a very high order filter (many poles) to merely approximate the theoretical optimum, and (2) the sin x/x time response must be maintained precisely matched to the sampling rate to avoid spurious artifacts (aliasing or moire effects). Two-dimensional implementation is even more impractical because of complexity and criticality of matching; with serious artifact generation resulting from only slight mismatching. Practical approximations to the ideal filter generate artifacts which are particularly noticeable when the image is moved, especially when the image is rotated.